The objectives of this research program are to elucidate the pathway of ubiquinone biosynthesis in eukaryotic cells with emphasis on: (a) the identity of the intermediates, (b) the nature of the enzymes involved in each step, including the mechanism of the reaction, and (c) the factors which regulate the pathway under various conditions. Ubiquinone biosynthesis occurs in rat liver and yeast mitochondria and hence efforts will be made to solubilize given enzymes in the biosynthetic sequence from this source. Eukaryotic cells appear to differ from prokaryotic cells in one aspect of the biosynthesis of ubiquinone, namely the decarboxylation system for prenylbenzoates. Prokaryotes decarboxylate the alkylbenzoates first whereas eukaryotes hydroxylate and methylate first and then decarboxylate to yield 6-methoxy-2-polyprenylphenol. Glucose repression of ubiquinone biosynthesis has been found to be mediated via a cyclic AMP protein kinase which converts an inactive methylase for 3,4-dihydroxy-5-hexaprenylbenzoate to the active form. Further studies will deal with isolation of the relevant protein kinase, study of its entry into mitochondria where it acts on the methylase in the inner mitochondria. The effect of compactin, an inhibitor of HMG-CoA reductase, upon the biosynthesis of ubiquinone-6 and ergosterol in yeast will also be studied. The first hydroxylase in the sequence, namely 4-hydroxy-5-polyprenylbenzoate hydroxylase, will be purified from yeast and rat kidney mitochondria.